The purpose of this project is to develop vaccines against otitis media caused by nontypeable Haemophilus influenzae (NTHi) and Moraxella catarrhalis. In this fiscal year, efforts are focusing on investigating the effect of active or passive immunization with M. catarrhalis strain 25238 detoxified lipooligosaccharide (dLOS)-protein conjugate vaccines or their antiserum on pulmonary clearance of the bacteria in an mouse aerosol challenge model. Mice were injected with dLOS-tetanus toxoid (dLOS-TT), or dLOS-high-molecular-weight proteins (dLOS-HMP) from NTHi, and challenged with M. catarrhalis strains 25238, 035E, or NTHi strain 12. Immunization with dLOS-TT or dLOS-HMP generated a significant rise of serum anti-LOS IgG, and a 68% and a 35-41% reduction of bacteria in lungs compared with control (p< 0.01) following challenge with homologous strain 25238 and a heterologous strain 035E, respectively. Serum anti-LOS antibody levels correlated with its bactericidal titers against M. catarrhalis and bacterial colony-forming units (CFU) in lungs. Additionally, immunization with dLOS-HMP generated a 54% reduction of NTHi strain 12 compared with the control (p<0.01). Passive immunization with a rabbit antiserum against dLOS-TT conferred a significant reduction of strain 25238 CFU in lungs in a dose- and time-dependent pattern compared with preserum-treated mice. Kinetic examination of lung tissue sections demonstrated that antiserum-treated mice initiated and offset inflammatory responses more rapidly than preserum-treated mice. These data indicate that LOS antibodies (whether active or passive) play a major role in the enhancement of pulmonary clearance of different test strains of M. catarrhalis in mice. In addition, dLOS-HMP is a potential candidate for a bivalent vaccine against M. catarrhalis and NTHi infections.